The bigger questions might be:
How long before aircrew get fed up with spy-in-the-cab?
Is it right and proper that a controller might query a pilot's actions or selections.....given that it is unlikely that the controller is qualified on type?
Are we turning ATC into a giant video game?
Do you want a couple of dozen label blocks the size of Greater London to distract you from the prime function of controlling?
Deafening silence from the "regulator" as usual.....this ends up with 50 controllers developing 50 different personal operating regimes...as usual!
P.S. At the moment, if a pilot fails to comply with an instruction or imposed limitation, the fault [if that is the appropriate word] might be identified as a pilot error. If it is the duty of the controller to cross-check or monitor any mode S indicator....then fault might be said to apply equally or partially with the controller. Do you want that?